Microcavities filled with biologically produced green fluorescent protein show polariton condensation at room temperature.

Exciton-polaritons are hybrid light-matter particles that form upon strong coupling of an excitonic transition to a cavity mode. As bosons, polaritons can form condensates with coherent laser-like emission. For organic materials, optically pumped condensation was achieved at room temperature but electrically pumped condensation remains elusive due to insufficient polariton densities. Here we combine the outstanding optical and electronic properties of purified, solution-processed semiconducting (6,5) single-walled carbon nanotubes (SWCNTs) in a microcavity-integrated light-emitting field-effect transistor to realize efficient electrical pumping of exciton-polaritons at room temperature with high current densities (>10 kA cm) and tunability in the near-infrared (1,060 nm to 1,530 nm). We demonstrate thermalization of SWCNT polaritons, exciton-polariton pumping rates ∼10 times higher than in current organic polariton devices, direct control over the coupling strength (Rabi splitting) via the applied gate voltage, and a tenfold enhancement of polaritonic over excitonic emission. This powerful material-device combination paves the way to carbon-based polariton emitters and possibly lasers.

Exciton-polaritons form upon strong coupling between electronic excitations of a material and photonic states of a surrounding microcavity. In organic semiconductors the special nature of excited states leads to particularly strong coupling and facilitates condensation of exciton-polaritons at room temperature, which may lead to electrically pumped organic polariton lasers. However, charge carrier mobility and photo-stability in currently used materials is limited and exciton-polariton emission so far has been restricted to visible wavelengths. Here, we demonstrate strong light-matter coupling in the near infrared using single-walled carbon nanotubes (SWCNTs) in a polymer matrix and a planar metal-clad cavity. By exploiting the exceptional oscillator strength and sharp excitonic transition of (6,5) SWCNTs, we achieve large Rabi splitting (>110 meV), efficient polariton relaxation and narrow band emission (<15 meV). Given their high charge carrier mobility and excellent photostability, SWCNTs represent a promising new avenue towards practical exciton-polariton devices operating at telecommunication wavelengths.

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two new hybridized modes appear-the upper (UP) and lower polariton (LP). These manifest in a characteristic anticrossing of the almost dispersionless exciton and the parabolic photon dispersion. From the dispersion of the polariton modes, the coupling potential (V A ), which is proportional to the observed minimal splitting between UP and LP, can be deduced. Organic materials favor particularly high coupling potentials (V A > 100 meV) due to their large oscillator strength and are ideal to create exciton-polaritons at room-temperature due to their large exciton binding energies. [1][2][3][4] The unique combination of both light and matter character in excitonpolaritons results in fascinating properties, for example, polaritons can reach a macroscopic occupation of the ground state (condensation) at room-temperature with coherent light emission, so-called polariton lasing, at lower thresholds than conventional photon lasing. [5][6][7][8][9] They may also affect chemical reactions and there have been suggestions that they can even influence charge transport. [10,11] Polariton emission typically occurs from the LP branch due to relaxation enabled by the excitonic character of the polaritons. Owing to their hybrid excitonic-photonic character, the emission linewidth of the LP is typically narrowed for many organic systems and can be spectrally tuned by adjusting the cavity resonance. [4] Further, if the coupling potential of the hybrid system exceeds about 20% of the exciton energy, the regime of ultrastrong coupling is reached, for which new intriguing phenomena are predicted and have also been observed to some extent. [12][13][14][15] Emission from the lower polariton in the ultrastrong coupling regime shows very low dispersion and thus minimal angular color shift while maintaining the narrow linewidth of the mixed state. [13,16] This feature makes the ultrastrong coupling regime attractive for color-pure emission from electrically driven lightemitting devices. Semiconducting donor-acceptor polymers show unusually high oscillator strength at low photon energies [17] and are thus ideal materials to achieve ultrastrong coupling. At the same time these polymers exhibit large ambipolar charge carrier mobilities, which render them interesting for electrical generation of exciton-polaritons. [18,19] In previous work light-emitting diode (LED) structures were used to achieve electrically driven exciton-polariton emission. In these structures, the cavity mirrors also acted as the injection electrodes. [15,[20][21][22][23][24] In case of organic LEDs (OLEDs), metallic anodes and cathodes (e.g., silver or aluminum) were Exciton-polaritons are quasiparticles with hybrid light-matter properties that may be used in new optoelectronic devices. Here, electrically pumped ultrastrongly coupled exciton-polaritons in a high-mobility donor-acceptor copolymer are demonstrated by integrating a light-emitting field-effect transistor into a metal-clad microcavity. Near-infrared electroluminescence is emitted exclusively from the lower pol...

The optical properties of organic semiconductors are generally characterised by a number of material specific parameters, including absorbance, photoluminescence quantum yield, Stokes shift, and molecular orientation. Here, we study four different organic semiconductors and compare their optical properties to the characteristics of the exciton-polaritons that are formed when these materials are introduced into metal-clad microcavities. We find that the strength of coupling between cavity photons and excitons is clearly correlated with the absorptivity of the material. In addition, we show that anisotropy strongly affects the characteristics of the formed exciton-polaritons

Fluorescence imaging is an indispensable tool in biology, with applications ranging from single‐cell to whole‐animal studies and with live mapping of neuronal activity currently receiving particular attention. To enable fluorescence imaging at cellular scale in freely moving animals, miniaturized microscopes and lensless imagers are developed that can be implanted in a minimally invasive fashion; but the rigidity, size, and potential toxicity of the involved light sources remain a challenge. Here, narrowband organic light‐emitting diodes (OLEDs) are developed and used for fluorescence imaging of live cells and for mapping of neuronal activity in Drosophila melanogaster via genetically encoded Ca2+ indicators. In order to avoid spectral overlap with fluorescence from the sample, distributed Bragg reflectors are integrated onto the OLEDs to block their long‐wavelength emission tail, which enables an image contrast comparable to conventional, much bulkier mercury light sources. As OLEDs can be fabricated on mechanically flexible substrates and structured into arrays of cell‐sized pixels, this work opens a new pathway for the development of implantable light sources that enable functional imaging and sensing in freely moving animals.

Given the prevalence of disorder in many organic semiconductors, the applicability of simple models to describe their behavior in the strong coupling regime, such as the two‐level coupled oscillator, is not evident. Here, the validity of the two‐level coupled oscillator model and the simple dependence of the coupling strength on the number of absorbers and the electric field is tested experimentally in metal‐clad microcavities containing a disordered film of small molecules. Multilayer microcavities are produced by combining different thin film deposition techniques. These allow for isolating the relevant parameters and thus to confirm the coupling strength is proportional to 1) the square root of the number of absorbers and 2) the amplitude of the electric field. By changing either of these two parameters, the microcavities are shifted from the weak to the strong coupling regime. Moreover, careful analysis reveals that there is a threshold coupling strength for the onset of the Rabi splitting. Two independent investigations show that this threshold is comparable to the losses in the cavities. These results validate the coupled two‐level Hamiltonian for microcavities containing disordered organic semiconductors, even though the assumption of a single exciton level represents a strong simplification for these systems.